Conventionally, minus-strand RNA viruses are harvested mainly by using a recombinant vaccinia virus expressing T7 RNA polymerase (vTF7-3: Fuerst, T. R. et al., Proc. Natl. Acad. Sci. USA 83, 8122-8126(1986), MVA-T7: Sutter, G. et al., FEBS lett. 371: 9-12 (1995)) and plasmids expressing NP, P, and L genes and minus-strand RNA viral genome under the control of a T7 promoter (Kolakofsky, et al., EMBO J. 14: 6087-6094 (1995); Kato, A. et al., Genes Cells 1: 569-579 (1996)). NP, P, and L, and antigenome RNA are supplied by the action of the T7 RNA polymerase expressed by the recombinant vaccinia virus. The cap structure is formed at 5′ ends of the NP, P, and L mRNAs through the action of a capping enzyme from the vaccinia virus. Then, the mRNAs are translated into proteins. The proteins interact with the antigenome RNA and constitute functional RNP. Then, genome RNP is replicated from the antigenome RNP. The viral proteins are also translated, and the infection cycle is initiated. The virus is then harvested.
The minus-strand RNA viral vector can be harvested by using a recombinant vaccinia virus. However, the vaccinia virus must be removed for the final vector preparation. This is costly and time-consuming. From the viewpoint of safety, it is desirable not to use a vaccinia virus for harvesting a vector if it is intended to be used as a vector for gene therapy.    Non-patent Document 1: Fuerst, T. R. et al., Proc. Natl. Acad. Sci. USA 83, 8122-8126 (1986)    Non-patent Document 2: Sutter G, et al, FEBS lett. 371: 9-12 (1995)    Non-patent Document 3: Kolakofsky et al., EMBO J. 14: 6087-6094 (1995)    Non-patent Document 4: Kato, A. et al., Genes Cells 1: 569-579 (1996)